Download The Physical Nature of Cosmic Accretion of Baryons and Dark Matter

The Physical Nature of
Cosmic Accretion of
Baryons & Dark Matter into
Halos and their Galaxies
Andrew Wetzel
Moore Fellow
Carnegie Fellow in Theoretical Astrophysics
Wetzel & Nagai 2014 arXiv:1412:0662
Spineto, Italy
June 2015
Outline
1. Physical Cosmic Accretion of Dark Matter
2. Physical Cosmic Accretion of Baryons
Andrew Wetzel
Caltech - Carnegie
58 picture of cosmic accretion
WECHSLER
ET AL.
Standard
into
halos
1.0
Wechsler et al 2002
1.0
M/M0
M/M0
0.5
0.1
0.1
1.0
0.5
a
Scale factor = 1/(1+z)
Andrew Wetzel
Fig. 4.—Average mass accretion histories, normalized at a ¼ 1. Left: binned
in three bins
by final halo m
Caltech
- Carnegie
log Physical Density
Physical nature of cosmic accretion into galactic halos
log Physical Radius
see Diemand et al 2007, Cuesta et al 2008, Diemer et al 2013
Andrew Wetzel
Caltech - Carnegie
log Physical Density
Physical nature of cosmic accretion into galactic halos
200 x background at given redshift
“pseudo-evolution”
200 x background at given redshift
log Physical Radius
see Diemand et al 2007, Cuesta et al 2008, Diemer et al 2013
Andrew Wetzel
Caltech - Carnegie
spherical region is sufficiently overdense, its gr
hin a halo. However,
Physical
Cosmic
self-attraction
overcomes
the
initial cosmolog
me level of gas accresion, such that
a mass shell
reach
a maxim
ime, suggesting that
Accretion
ofwill
Dark
Matter
and then collapse. Specifically, for flat ⇤CDM
ay not extend to gas.
(simulation
of
only
dark
matter)
the
radial
acceleration
around
some
overdens
ure of cosmic accrefor the evolution of
d2 r
G m(< r) 8⇡G
cosmic time, espe=
+
⇢
r
⇤
2
2
dt
r
3
example, galaxies at
3
% of their mass since
in which r is the physical radius from the ce
to determine of
the enclosed
overdensity
inside the splash- m(< Adhikari,
Dalalenclosed
& Chamberlain
2014 G is
ate of decline
the
overdensity,
r)
is
the
mass,
back radius, ∆ . Our results do not strongly depend on
s
our assumed mass profile inside the halo. For example,
using an isothermal profile instead of NFW gives results
that are consistent at the ∼ 10% level. Figure 2 shows the
predicted values of the enclosed overdensity. Throughout
this paper, we define overdensities relative to the mean
matter density, not the critical density. In our model,
∆s depends only on the halo’s accretion rate s, along
with the values of the background cosmological parameters ΩM and ΩΛ at the time the halo is observed. The
behavior we find is unsurprising. As the accretion rate is
increased (larger s), the potential deepens more quickly
in time, resulting in splashback occuring at a smaller radius, or equivalently, at a larger enclosed overdensity ∆s .
Similarly, at low redshift when ΩM diminishes and ΩΛ
increases, the mean background density of the universe
ρ̄m decreases more during the time between turnaround
and splashback, again resulting in a larger ∆s .
Finally, although the model presented here is exAndrewtremely
Wetzel
simple to evaluate, we also provide a very rough
radius
Caltech e=0.1
- Carnegie
Physical Cosmic Accretion of Dark Matter
from simulation with only dark matter
Andrew Wetzel
Caltech - Carnegie
Outline
1. Physical Cosmic Accretion of Dark Matter
2. Physical Cosmic Accretion of Baryons
Andrew Wetzel
Caltech - Carnegie
Physical accretion of gas & dark matter
from simulation with gas - non-radiative
Andrew Wetzel
Caltech - Carnegie
Physical accretion of baryons & dark matter
from simulation with star formation + thermal feedback
Andrew Wetzel
Caltech - Carnegie
Physical significance of R200m?
Andrew Wetzel
Caltech - Carnegie
Physical accretion of baryons & dark matter
from simulation with star formation + feedback
Andrew Wetzel
Caltech - Carnegie
Physical Cosmic Accretion of Dark Matter & Baryons
Dark matter growth is subject to pseudo-evolution
at z <~ 1, no significant growth of mass at any radius
Baryon growth is not subject to pseudo-evolution
Physical growth at all radii because gas is dissipational
Accretion rate at all r < R200m (nearly) tracks that at R200m
Accretion radius of low-mass halos not increase at z <~ 1
Most meaningful radius to measure cosmic accretion of both
dark matter and gas is ~2 R200m(z)
Andrew Wetzel
Caltech - Carnegie